Science Musings Blog

Friday, August 07, 2009

Where we came from

Author Doris Lessing began her sci-fi chronicle of space with this dedication: "For my father, who used to sit, hour after hour, night after night, outside our home in Africa, watching the stars. 'Well,' he would say, 'if we blow ourselves up, there's plenty more where we came from.'"

Oh, there's plenty more, all right; stars spangle the sky in uncountable numbers. And they're blowing up all the time.

Here's one that appeared on APOD the other day, the remnant of a star that blew itself up in 1006 AD Earth-time. Since the star was 7000 light-years away, it actually exploded 7000 years before it suddenly became visible in Earth's sky. APOD calls it the brightest supernova in recorded human history.

What we see today, a thousand years later, is this gorgeous bubble of star-stuff, still expanding, against the star-spangled background of more distant stars in the galaxy.

Human life is short compared to the lifespans of even the most short-lived stars. Lessing's father, in a lifetime of watching the sky, would be unlikely to see more than a few dying stars blow up. In my lifetime, I have seen only one stellar eruption, the nova of August 1975, which for one glorious evening blazed almost at bright as the nearby star Deneb in the constellation Cygnus, like a feather plucked from the swan's tail. Over the next week it faded to invisibility.

The most famous supernova of recent times was visible to the unaided eye for a few months during the first half of 1987, but only for observers south of the equator. It was a very big bang as stellar explosions go, but it was rather far away, in a small companion galaxy of the Milky Way, and never became bright enough to dazzle the backyard skywatcher. I count myself lucky to have seen the "new star" of 1975. And even luckier to have access to images such as the one above. These terrible and beautiful remnants of exploded stars are indeed "where we came from."